Titanic destroyer (7)
I believe the answer is:
iceberg
'titanic destroyer' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
This is all the clue.
Can you help me to learn more?
(Other definitions for iceberg that I've seen before include "Mass calved from a glacier" , "shunned by sailors?" , "Mass carved from a glacier" , "Hazard in Arctic sea" , "Floating mass (of lettuce?)" .)